Optical sensor for detecting articles in a monitored region and method for operating the same

ABSTRACT

An optical sensor device for detecting reflecting objects (11) has a light pulse emitter (12) and a light receiver (13) connected to an evaluation circuit (14) having a pulse generator (17) and a reception signal processing stage (24) which only emits an object detection signal when the light pulses or light pulse sequences received by the light receiver (13) lie above a switching threshold. The evaluation circuit (14) has a pulse emission influencing and triggering stage (15) connected in parallel to the reception signal processing stage (24) which triggers the emission of the following light pulse by the pulse generator (17) only when a detected variable disturbing signal has disappeared.

BACKGROUND OF THE INVENTION

The invention relates to a method for the operation of an optical sensorarrangement for detecting articles present in a monitored region using apulsed light transmitter which transmits light pulses with a timespacing one after the other into the monitored region. A light receiverreceives light and in the absence of articles to be detected receivessubstantially no light. When articles are in the monitored region thelight receiver receives light and a processing stage connected to thelight receiver transmits an article detection signal.

In the optical sensor arrangements with pulsed operation one isconcerned in the broadest sense with light barriers, i.e. reflex lightbarriers, light sensors, distance sensors, visibility measuring devicesetc. fall under this term. It is important that an optical sensorarrangement in accordance with the invention receives a light signalwhen an article to be detected is located in the monitored region andreceives no light signal when no article to be detected is present inthe monitored region. The invention can in particular be used withadvantage when the non-detection of an article guided through themonitored region is unproblematic, i.e. does not for example involve adangerous state, and in which the presence of an article in themonitored region may in no case be signalled when such an article is notpresent there.

The invention is primarily used where, for example, articles to becounted such as ampoules or packages pass one after the other throughthe monitored region and where the presence of an article in themonitored region may under no circumstances be simulated.

Optical sensor arrangements, in particular light barriers for therecognition of articles generally operate in accordance with the pulsedprinciple in which a light pulse is transmitted periodically for a shortduration and the light reflected from the article is received by thelight receiver and evaluated in the evaluation circuit. Each transmittedlight pulse can for example have a time length of the order of magnitudeof 1 to 10 μs. A comparatively long pause, which can correspond toapproximately ten to one hundred times the value of the transmittedpulse length, then follows each transmitted light pulse. The use oflight pulses has two advantages. On the one hand, an improvedsignal/noise ratio is achieved in comparison with a continuoustransmitter operation with the same power losses. On the other hand, theinfluence of constant light can be illuminated in simple manner by theinsertion of a high pass filter into the received signal processingstage.

Problematic with such pulsed reflex light barriers is however the factthat disturbing signals which change with time, in particular disturbingpulses, can lead to a falsification of the evaluation result when theyoccur precisely during the sending of a transmitted light pulse andenter via an optical or electromagnetic path into the evaluationcircuit. The disturbing signals can be both optical disturbing signalsor also electromagnetic disturbances which can be coupled into theelectronic part of the reflex light barrier following the optoelectronicconversion in the light receiver.

For this reason one has already attempted to restrict the influence ofdisturbing signals by filters which follow the light receiver which donot transmit every received signal as a detection signal. These measureshave however the disadvantage that only a received light value averagedover a specific time period is evaluated. The effective switchingfrequency of the actual signal is thereby reduced in undesirable manner.

SUMMARY OF THE INVENTION

The invention is based on the object of providing a method and anarrangement of the initially named kind which with an unchanged outputswitching frequency, are substantially more resistant to disturbance andwhich permit an ideal elimination of disturbances, in particular withdisturbing signals which occur frequently such as disturbing light.

In order to solve this object the features of present invention areprovided. After transmitting a switched off and the output signal of thelight receiver is investigated, at least in the end region of thesubsequent pause until the next transmitted pulse, as to whether avarying disturbing signal is present. Upon finding a varying disturbingsignal the transmission of the next transmitted pulse is shiftedtimewise by an amount such that on transmitting the next transmittedpulse the disturbing signal has sunk at least with a certain probabilitybelow the response threshold of the received signal processing circuit.Alternatively, a disturbance detection stage can be provided which isconnected to the light receiver and causes, upon detecting reception ofa variable disturbing signal, a subsequent transmitted pulse influencingor trigger stage to trigger the transmission of the next transmittedpulse by the pulse generator activated by the transmitted pulseinfluencing or trigger stage only after the actual or probable end ofthe varying disturbing signal. A controlled change-over switch isinserted in the path between the light receiver and the received signalprocessing stage. The change-over switch is switched so that is connectsthe light receiver with the received signal processing stage only on thetransmission of a transmitted pulse by the pulse transducer. Incontrast, in the pause between two transmitted pulses, the change-overswitch connects the light receiver at least shortly before thetriggering of the next transmitted pulse, preferably during the entiretime interval between the sending of two sequential transmitted pulses,to the disturbance stage or to the transmitted pulse influencing ortrigger stage.

The basic concept of the invention lies in the fact that the transmittedlight pulses are not rigidly periodically transmitted but rather theirtransmission is made dependent on the occurrence of the disturbingsignal scattered in from the outside. For this purpose a received signalis also detected in times at which no transmitted light pulse istransmitted and thereby information is obtained concerning theenvironment. Through a suitable algorithm an ideal transmission timepoint can then be determined at which no disturbing signal isinstantaneously present, at least with a high probability. The measuresof the invention thus extensively prevent a disturbing signal comingfrom the outside simulating the presence of an article in the monitoredregion. Only in the most extreme case is it possible, if a varyingdisturbance should endure for a long period, for the recognition on anarticle to be totally missed, if the article has been moved out of themonitored region again during this time. The invention is thus inparticular applicable with particular advantage where the simulation ofthe presence in an article may under no circumstances occur, but theoccasional non-recognition of an article due to a transmitted lightpulse being omitted for too long a time is not disturbing.

In a preferred embodiment, a specific transmitted pulse is onlytransmitted a predetermined time after the preceding transmitted pulseswhen no disturbing signal is present shortly before the intended time oftransmission. In the presence of such a disturbing signal thetransmission of the transmitted pulse is shifted by a predetermined timewhich preferably corresponds to the fixed time interval present betweentwo transmitted pulses in the disturbance-free case. The transmission ofthe transmitted pulse after even this time only then takes place when adisturbing signal has not been found shortly before it.

For statistically occurring disturbances it is advantageous to check thepresence of a disturbing signal several times between two transmittedpulses.

If, in contrast, a previously known disturbance problem exists whichconsists in particular in disturbances of periodic character which occurin accordance with a predetermined pattern one can expediently proceedin accordance with another embodiment of the invention. Upon detecting adisturbance with periodic character during the disturbed light receivingperiods between the transmitted light pulses, the transmission of thelight pulses is effected so that the transmission takes place in thecenter region of the disturbance-free periods.

A particularly advantageous embodiment investigates the change of theamount and direction of the disturbing signal with respect to twodifferent thresholds, or by means of a differentiation element. Thetransmission of a transmitted pulse then only taking place when thedisturbing signal reduces, with that value of the disturbing signalpreferably being extrapolated where the disturbing signal should reduceto zero, and with the transmission of the transmitted pulse first takingplace after this value. In a further embodiment the received signal ofthe light receiver is time-averaged over a long time after a transmittedpulse. The next transmitted pulse is only triggered a when, after apredetermined time, the signal falls beneath a predetermined value. Inanother embodiment the response threshold for the detection of adisturbing signal lies substantially lower than the response thresholdof the received signal processing stage.

With an optical sensor arrangement in accordance with the the clockingof the received signals. Another advantageous embodiment ischaracterized in that a clock generator, with a frequency of a higherorder of magnitude than the normal light pulse frequency, digitizes thereceived signal. The individual received pulses formed in this way areinvestigated in the transmitted pulse influencing or trigger stage forthe presence or absence of a disturbance. The triggering of atransmitted pulse in the pulse transducer is caused via the transmittedpulse influencing or trigger stage when no disturbance has been foundwith a predetermined number of preferably sequential received pulses.

The transmitted pulse influencing or trigger stage preferably includes apulse step down stage connected to the clock generator which firsttriggers a transmitted pulse only after a plurality of in particular 50to 100 clock pulses. Upon the occurrence of only one disturbed receivedpulse the disturbance detection stage prevents the initiation of atransmitted pulse through the pulse step down stage, or through thetransmitted pulse influencing or trigger stage, until the predeterminednumber of undisturbed received pulses has been found.

The clock generator preferably clocks a digital integrator connected tothe transmitted pulse influencing or trigger stage representing thedisturbance detection stage. The clocked received signal is evaluated inaccordance with disturbance or non-disturbance being connected to thedigital integrator and with the latter causing the transmitted pulseinfluencing or trigger stage to initiate a transmitted pulse in thepulse transducer only on the presence of a specific number ofdisturbance-free received pulses. The digital integrator is reset tozero after the occurrence of only a single disturbed received pulse andwith a transmitted pulse only then being triggered when the digitalintegrator has counted a predetermined number of undisturbed receivedpulses.

The output signal of a likewise clocked comparator with a fixedthreshold to which the received pulses are supplied is connected to theresetting input of the digital integrator.

A more sensitive triggering can take place in accordance with thefollowing embodiments. The output signal of a preferably clockedcomparator, to which a two stage threshold signal is supplied from thedisturbance detection stage, is applied to the disturbance detectionstage and switches between two threshold values when the disturbedsignal only falls short of the upper threshold and switches to the lowerthreshold value when the signal also does not reach the lower threshold.The transmitted pulse is only triggered thereafter, and indeedpreferably that much later the longer the disturbing signal adopts avalue between the two thresholds.

The following defines preferred practical embodiments of the opticalsensor arrangement in accordance with the invention. The transmittedpulse trigger stage has, following an amplifier fed by the lightreceiver, two comparators with different thresholds and connected inparallel. When the received signal forms short of the upper threshold aninternal signal increase is triggered in a subsequent threshold timecircuit with an attached comparator and wherein, on also falling shortof the lower threshold, an external signal output to the comparator iseffected which continuously reduced from the achieved signal increasevalue. The reduction preferably being linear. A transmitted pulse istriggered only when the external signal of the threshold timing circuitfalls short of the threshold of the comparator.

The optical sensor arrangement may also have, following an amplifierwhich is fed by the light receiver, a first comparator with a firstthreshold and connected in parallel with a differentiating circuit. Theoutputs are supplied to the two inputs of a sample and hold circuitwhich follows a voltage current converter with a subsequent chargingelement, in particular a capacitor. The charging element, upon achievinga predetermined voltage, causes, via a comparator with a threshold, thetransmission in the transmitted pulse influencing or trigger stage of atransmitted pulse trigger signal to the pulse generator.

The optical sensor arrangement may also have a mean value forming stage,for example a low pass filter, acting on the transmitted pulseinfluencing and trigger stage provided following an amplifier fed by thelight receiver. The mean value forming stage triggers a transmittedpulse in the pulse generator via the transmitted pulse influencing ortrigger stage when, after a specific time since the last transmittedpulse, the means value falls below a predetermined threshold. In so faras transmitted pulses are absence for longer periods of time as a resultof disturbances care should be taken in accordance with the inventionthat in this case the operating person is made aware of this fact by analarm signal. Optical sensor arrangement preferably includes a missingpulse detection stage which triggers an alarm device in the absence of atransmitted pulse within a predetermined time interval after thetransmission of the last transmitted pulse. Such an alarm signal shouldbe preferably be given in a transmitted pulse, transmitted displaced bymore than one period of the normal transmitted pulse sequence. It isalso possible to provide a stepped alarm arrangement in such a way thatwith a comparatively small pulse delay from a half to a whole period andin that a second alarm stage only then responds when a transmitted pulseis transmitted which is delayed by a multiple of the normal pulsesequence period.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a circuit diagram of the principle of a reflex light barrier inaccordance with the invention,

FIG. 2 two intensity time diagrams to illustrate the function of thearrangement of FIG. 1,

FIG. 3 a block circuit diagram of a digitally operating reflex lightbarrier in accordance with the invention,

FIG. 4 a block circuit diagram of a further embodiment, the function ofwhich is explained with respect to the three intensity time diagrams ofFIG. 5,

FIG. 6 a block circuit diagram of a further embodiment, the function ofwhich is explained with respect to the four intensity time diagrams ofFIG. 7,

FIG. 8 a block circuit diagram of a further embodiment, the function ofwhich is explained with respect to the three intensity time diagrams ofFIG. 9,

FIG. 10 a block circuit diagram of an embodiment which is somewhatmodified relative to FIG. 3,

FIG. 11 three intensity time diagrams to illustrate the function of theblock circuit of FIG. 10, and

FIGS. 12 to 14 a schematic illustration of three different light barriertypes with which the invention can be used with advantage.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 12 shows schematically a reflection light barrier with anevaluation circuit 14 having an output 44 and which supplies a pulseslight transmitter 12 with voltage pulses so that the latter can transmitlight flashes 47 into a monitored region 47. If an article 11 to bedetected and having a surface 11' which specularly or scatteringlyreflects light is present in the monitored region 47 then a part of thepulsed light will be deflected to a light receiver 13 arranged directlyalongside the pulse light transmitter. The corresponding output signalis supplied to the evaluation circuit 14 and investigated to see whetheran article 11 is present or not in the monitored region 47. By way ofexample an electrical L-signal can appear at the output 44 when anarticle 11 is detected in the monitored region 47. It is for examplepossible with reflected light barriers to detect articles which pass oneafter the other through the monitored region 47 and for example to countthem. Such reflex light barriers are for example used for articledetection in the production of ampoules or flasks.

In accordance with FIG. 13 the pulsed light transmitter 12 and the lightreceiver 13 can also be arranged opposite to one another when the lightimpinges shallowly onto the reflecting surfaces 11' of the articles 11in the monitored region 47 and passes from there to the light receiver13. It is important that in this case also the light receiver 13 isconnected to the evaluation circuit 14 which feeds the pulsed lighttransmitter 12.

Another possibility of applying the invention is given in the lightbarrier of FIG. 14 where transparent articles are passed one after theother in the direction of the arrow between the light transmitter 12 andthe light receiver 13, with non-transparent regions formed for exampleby a diaphragm 60 being located between the transparent articles. As thetransmitted light pulses can be very shifted substantially as a resultof the invention described in detail in the following, depending on thepresence or absence of disturbing light amongst other things, it isimportant in all applications of the invention that the non-recognitionof individual articles as a result of light pulses of delayed appearanceshould not lead to dangerous or non-acceptable circumstances.

In accordance with FIG. 1 an optical sensor arrangement in accordancewith the invention which is formed as a reflex light barrier has a pulsetransmitter 12 which for example transmits transmitted light pulses offor example 5 μs length which, in the absence of disturbing signals, canhave a constant time interval of for example 50 times the pulse length.

If a light reflecting article 11 is present in the monitored region 47of the reflex light barrier then it reflects the incident light of thetransmitted light pulses partly to a light receiver 13 which isconnected via a high pass filter 18 to an evaluating circuit 14 in whicha received signal processing stage 24 is located. The received signalprocessing stage 24 is connected via a controllable change-over switch25 with the light receiver 13 and which has a comparator 19 acted on bya threshold signal 20 which determines whether an incoming pulse or anaverage value of several sequentially incident pulses is larger orsmaller than the preferably adjustable threshold signal 20. If themeasurement signal which is detected by the comparator 19 is larger thanthe threshold signal 20 then an article detection signal appears at theoutput 44.

The control input 68 of the control change-over switch 25 is connectedto a pulse generator 17 which causes the pulsed light transmitter 12 totransmit transmitted light pulses. Each time when a transmission pulse45 is transmitted to the pulsed light transmitter 12 so that the lattertransmits a transmitted light pulse, the change-over switch 25 isbrought briefly, via a signal supplied from the pulse generator 17 toits control input 68, into the position illustrated in broken lines inFIG. 1 where it connects the light receiver 13 with the received signalprocessing stage 24, so that the signal received during the duration ofa transmitted light pulse from the light receiver 13 can be evaluated inthe received signal processing stage 24 in the customary manner.

During the remaining times the change-over switch 25 is in the positionillustrated in continuous lines in FIG. 1 in which the light receiver 13is connected with a disturbance detection stage 46 which acts on atransmitted pulse influencing or trigger stage 15 which is in turnconnected to the pulse generator 17. The disturbance detection stage 46,the transmitted pulse influencing or trigger stage 15 and the pulsegenerator 17 together form the transmission stage 26. The receivedsignal processing stage 24, the change-over switch 25 and thetransmission stage 26 together form the evaluation circuit 14.

In so far as no varying optical disturbing signals 21 or electromagneticdisturbing signals 22 act on the receiver part, or on the evaluationcircuit 14 of the reflex light barrier of FIG. 1 the transmitted pulseinfluencing or triggering stage 15 initiates a transmitted pulse 45 atconstant time intervals of, for example, 250 μs, which causes acorresponding transmitted light pulse of the pulsed light transmitter12. For each transmitted pulse 45 the change-over switch 25 switchesinto the position illustrated in broken lines in FIG. 1 so that duringeach transmitted pulse an evaluation of the received light can takeplace in the received signal processing stage 24.

In the pauses between two transmitted light pulses the change-overswitch 25 is in the position shown in continuous lines so that in thesetime periods the output 44 of the received signal processing stage 24 isnot influenced by any electrical output signals at the light receiver.Such varying disturbing signals which can be generated by disturbinglight 21 or by electromagnetically disturbing relation 22 do howeverpass into the disturbance detection stage 46 which then causes thetransmitted pulse influencing or trigger stage 15 to prevent or delaythe triggering of the next transmitted pulse in the pulse generator 17and indeed for so long until the disturbance detection stage 46 actuallydetects the termination of the disturbance or the termination of thedisturbance is detected as being probable from specific measured values.At the point in time where the disturbance is actually terminated andwhere its end probably occurs the transmitted pulse influencing ortrigger stage 15 is caused by the disturbance detection stage 46 toinitiate the next transmitted pulse at the pulse generator 17.

In the simplest case the transmitted pulse influencing or trigger stage15 can be an oscillator operating at the frequency of the pulsesequence, the pulses of which are suppressed when a disturbing signal isdetected by the disturbance detection stage 46 shortly before theirtransmission.

As, in the latter case, a whole period of the pulse sequence is howeverlost for the measurement, it is preferred if, on detection on adisturbing signal through the disturbance detection stage 46, thetransmitted pulse influencing or trigger stage 15 is caused to onlydelay the triggering of the next transmitted pulse which is actually dueonly until the disturbing signal has at least largely died away.

This is diagrammatically illustrated in FIG. 2. In the lower diagram thetransmitted pulses which are normally initiated by the transmitted pulseinfluencing or trigger stage 15 at the pulse generator 17 areillustrated in broken lines at 45.

In the upper diagram two disturbing pulses 66 are reproduced which canbe coupled either optically (21 in FIG. 1) or electromagnetically (22 inFIG. 1) into the reception precisely during the times at which thetransmitted pulses 45 which are used for the measurement should actuallyoccur.

As a result of the method of the invention the transmitted pulses arehowever now in each case displaced until the disturbing pulse 66disappears so that they actually occur at the positions 45' in FIG. 2where no disturbing signals are any longer present. In this manner adisturbance-free reception is ensured during the times of thetransmitted pulses.

The second displaced transmitted pulse 45' in the lower diagram of FIG.2 is again followed by a normal transmitted pulse 45 in the given normalinterval A. Transmitted pulses 45 then subsequently occur again at thepredetermined constant time intervals so long as no further disturbingsignal is received in a pulse gap.

In a simplified solution the transmitted pulses 45 are simply suppressedwhile the next pulse 45" provided in the given interval is againreleased by the transmitted pulse influencing or trigger stage 15.

Thus, in any event, a comparatively long pause is provided between thetransmitted pulses. Only after the expiry of the long pauses are thetest light receptions preferably carried out. A continuous signalevaluation is also actually possible, however for thermal reasons of thetransmitter stage 26 at least the long pause must always be given for anew light pulse.

In accordance with FIG. 1 a pulse drop out detection stage 54 is alsoconnected to the pulse generator 17 which is in turn connected with analarm apparatus 55 of an optical or acoustic nature. In this way analarm signal can be transmitted when a transmitted pulse 45 which isactually due has still not occurred after a specific interval beforebenefits become available. The operating person is hereby made aware ofthe delayed or possibly totally no longer existing operability of thesensor arrangement.

FIG. 3 shows a digitally operating embodiment in which the samereference numerals designate the same components as in FIG. 1. Theoutput signal of the light receiver 13 is applied via an amplifier 34containing a high pass filter 18 and eventually an integrator 49 to aclamping switch 67 which is connected to a comparator 48 with areference threshold 69.

The output signal of the comparator 48 is applied via the change-overswitch 25 in parallel to the received signal processing stage 24 and tothe transmitter stage 26 which, as in FIG. 1, contains the transmittedpulse influencing or trigger stage 15 and the pulse generator 17.

A digital integrator 16 for example in the form of a counter, isprovided in the transmitted pulse influencing or trigger stage 15 as adisturbance detection stage. On the one hand, the output signal of thecomparator 48 is supplied to the digital integrator 16 and, on the otherhand, the clock signal of a clock generator 23 is supplied to thedigital integrator, the clock generator 23 also clocking (timing) theswitch 67 and the comparator 48. The frequency of the clock generator 23amounts to many times, for example 50 to 100 times the transmitted pulsefrequency in the case of non-presence of disturbing signals.

In so far as a disturbing signal occurs between the transmitted pulsesthe latter is applied, as a result of the periodic closing of theclamping switch 67 brought about by the clock generator 23, to the inputof the comparator 48 which in each case transmits a pulse output signalapplied to the input I of the digital integrator 16 when the disturbanceexceeds the reference threshold 69.

As long as no disturbance is present the counter or digital integrator16 counts the beats of the clock generator 23 because then the absenceof a resetting signal at the input II of the digital integrator 16signalises freedom from disturbance. On the occurrence of the disturbingsignal at the output of the comparator 48 the counter is reset. Atransmitted pulse is first triggered through the transmitted pulseinfluencing or trigger stage 15 when the digital integrator 16 hasachieved a predetermined positive and in particular presettable count+N. This states namely that a defined number of test light receptionshas occurred free of disturbance.

A substantially more differentiated evaluation is possible with thecircuit of the transmitted pulse influencing or trigger stage 15 of FIG.4. There the output signal of the light receiver 13 is applied via anamplifier 34 in parallel to two comparators 27, 28 which, in accordancewith the upper diagram in FIG. 5, have two thresholds 29, 30 ofdifferent heights.

The outputs of the two comparators 27, 28 are applied to the two inputsof a threshold time element 31 which is nudged into action on beingexposed to an output signal of the comparator 28 having the higherthreshold 30 and which transmits an output signal which rises inaccordance with the center diagram in FIG. 5 (time points t₁ and t₂). Ifthe disturbing signal subsequently exceeds again the threshold (timepoint t₄) then the threshold time circuit 31 is again reset internally.

If however the comparator 27 responds as a result of the signal fallingshort of the threshold 29 then the already integrated time value (t₃) isused in order to find the point at which the light transmission shouldtake place, i.e. at which the disturbance would reduce to zero if theassumed linear drop off continues. A comparator 33 with the threshold 32and connected to the threshold time circuit 31 detects when the signalfalls below the threshold 32, which can be zero. In this way atransmitted pulse trigger signal is transmitted to the pulse generator17 via the transmitted pulse influencing or trigger stage 15 so that thepulse generator 17 transmits the transmitted pulse signal 45' reproducedin the lower diagram of FIG. 5.

A disturbing signal is reproduced in the upper diagram of FIG. 5 whichhad for the first time already fallen below the upper threshold at anearlier time t₁, whereby the threshold time circuit 31 is also caused toincrease an internal integration voltage 51. As the disturbing signalhowever subsequently exceeds the threshold 30 again the threshold timecircuit 31 is again reset internally to its output value without leadingto the triggering of the comparator 33.

Only when the passage of the signal through the upper threshold 30 fromabove to below at the time t₂ is followed by a time t₃ at which thesignal also passes through the lower threshold 29 at the time t₃ is thethreshold switching member 31 internally so switched over that alinearly reducing output voltage 50 (FIG. 5) appears at its output.

The increase of the gradient which reproduces the output potential 50must be sufficiently small that the signal only falls short of the lowerthreshold 32 when the disturbing signal has already become zero at atime t. The duration of the presence of the disturbing signal betweenthe thresholds 29, 30 thus influences in advantageous manner thetriggering of the transmitted pulse.

The embodiment of FIGS. 6 and 7 operates following the amplifier 34 witha comparator 36 which has a threshold 39 and which is connected inparallel with a differentiating circuit 35. The outputs of thedifferentiating circuit 35 and of the comparator 36 are connected to thetwo inputs of a sample and hold circuit 37 which is followed by avoltage current converter 61 with a subsequent capacitor 38 which isrechargeable with a predetermined time constant in accordance with theoutput signal of the circuit 37. The capacitor 38 is connected to thetransmitted pulse influencing or trigger stage 15.

The capacitor 38 is connected to a further comparator 59 with thethreshold 40 (see also FIG. 7) which then transmits a correspondingsignal to the transmitted pulse influencing or trigger stage 15 when thevoltage of the capacitor 38 exceeds the reference value 40 with thetransmitted pulse influencing or trigger stage 15 then accordinglytriggering the transmitted pulse.

In accordance with FIG. 7, uppermost diagram, the disturbing signalreceived at the light receiver 13 has a tendency to drop away steeply.The differentiated signal at the output of the differentiating circuit35 is reproduced in the second diagram from the top in FIG. 7. If thecomparator 36 detects that the disturbing signal has fallen below thethreshold 39, then a signal is transmitted to the sample and holdcircuit 37 which, in accordance with the second diagram from the top inFIG. 7 causes the output signal of the differentiating circuit 35 to beheld in the sample and hold circuit 37. At the same time the start ofthe charging of the capacitor 38 is initiated by the circuit 37 which isillustrated in the third diagram from the top in FIG. 7.

As soon as the voltage at the capacitor 38 in accordance with the thirddiagram from the top in FIG. 7 has exceeded the threshold 40 thetransmitted pulse influencing or triggering stage 15 is caused by thecomparator which detects this to transmit a trigger signal which in turncauses the pulse generator 17 to send a transmission pulse to the pulsedlight transmitter 12. The transmitted pulse 45' is schematicallyreproduced in the lowermost diagram of FIG. 7.

FIG. 8 shows a further possibility for eliminating disturbing signals bysuitable shifting of the transmitted pulse 45'.

Here the output signal of the amplifier 34, which in this case cancontain a high pass filter, is applied in rectified form to a low passfilter 41 which represents a mean value forming stage which operates inaccordance with the middle diagram of FIG. 9 in so far as the disturbingsignals illustrated schematically in the uppermost diagram of FIG. 9 arepresent. An output signal which exceeds the threshold 43 is present atthe output of the low pass filter 41 which has only died awaysufficiently that it falls below the threshold 43 again, a certain timeafter termination of the last disturbing signal. This is determined bythe transmitted pulse influencing or trigger stage 15 which thentriggers the transmitted pulse 45' (lowermost diagram in FIG. 9) in thepulse generator 17.

FIG. 10 shows a modification of the circuit of FIG. 3 which resides inthat a reference line 58 having a two stage threshold signal isconnected to the reference input of the comparator 48 in place of afixed threshold 49, with the reference line being tapped off from thedisturbance detection stage 46 which is arranged before the transmittedpulse influencing or trigger stage 15 and which is acted on by theoutput of the comparator 48 and also by the clock generator 23.

In accordance with the uppermost diagram in FIG. 11 the disturbancedetection stage 46 is able to distinguish between an upper threshold 53and a lower threshold 56. If the disturbing signal reproduced in theuppermost diagram of FIG. 11 is first above the upper threshold 53 thena disturbing signal appears at the output of the comparator 48 whichinitially holds the disturbance detection stage 46 at an upper thresholdvalue 57 (see the second diagram from the top in FIG. 11). If thedisturbing signal falls below the upper threshold 53 then thedisturbance detection stage 46 first switches to a lower threshold value62. Accordingly the reference threshold of the comparator 48 is reducedvia the line 58. If now--as is assumed in FIG. 11 in the region III--thedisturbance lies between the thresholds 53 and 56 then this isrecognised by the disturbance detection stage 56 and it switches after ashort period of time to the upper threshold again etc. until in theregion IV (FIG. 11) the disturbance again exceeds the upper threshold53, whereupon the disturbance detection stage 46 is again firmly set tothe upper threshold value 57.

If the disturbing signal then again falls below the upper threshold 53in the region V then the to and fro switching of the disturbancedetection stage 46 between the threshold values 57 and 62 is firstrepeated until finally the disturbing signal falls below the lowerthreshold 56, whereupon the disturbance detection stage 46 remains atthe lower threshold value 62 and after a specific time initiates thetransmitted pulse 45 indicated in the lower diagram of FIG. 11.

In accordance with the invention the time t₀ between the time at whichthe signal falls below the lower threshold 56 and the triggering of thetransmitted pulse 45 can be made dependent of the length of the timet_(x) during which the disturbing signal is present between thethresholds 53 and 56. The longer this time interval t_(x) is the longershould be the time t₀ after which the transmitted pulse 45 is triggered.That is to say, that with rapidly decaying disturbances the transmittedpulse 45 is initiated a relatively short time after the signal fallsbelow the lower threshold 56, whereas with long enduring disturbancesbetween the thresholds 53 and 56 the time until the transmitted pulse 45is initiated, is correspondingly lengthened.

The circuit of FIG. 10 thus discloses a further possibility as to howthe speed of reduction of the disturbing signal can be taken intoaccount with more or less delayed initiation of the transmitted pulse45.

We claim:
 1. Method for the operation of an optical sensor arrangementfor the detection of articles present in a monitored region with apulsed light transmitter which transmits light pulses with a timespacing one after the other into the monitored region and with a lightreceiver which in the absence of articles to be detected receivessubstantially no light from the light receiver, but which on thepresence of an article to be detected in the monitored region receivesso much light from the light transmitter by reflection or transmissionthat a received signal processing stage connected to the light receivertransmits an article detection signal, characterised in that aftertransmitting a transmitted light pulse the received signal processingstage (24) is switched off and the output signal of the light receiver(13) is investigated, at least in the end region of the subsequent pauseuntil the next transmitted pulse (45), as to whether a varyingdisturbing signal is present; and in that on finding a varyingdisturbing signal the transmission of the next transmitted pulse isshifted timewise by an amount such that on transmitting the nexttransmitted pulse the disturbing signal has sunk at least with a certainprobability below the response threshold of the received signalprocessing circuit (24).
 2. Method in accordance with claim 1,characterised in that the result of a transmitted light pulse istemporarily stored and an article detection signals is only thentriggered when an article was recognised and at the same time novariable disturbing signal was determined not only prior to but alsoafter transmission of the transmitted light pulse.
 3. Method inaccordance with claim 2, characterised in that the durations of the timeintervals investigated for the presence of a variable disturbing signalprior to and after transmission of the transmitted light pulse are ofthe same size.
 4. Method in accordance with claim 1, characterised inthat a specific transmitted pulse is only then transmitted apredetermined time after the preceding transmitted pulses when nodisturbing signal is present shortly before the intended time oftransmission; and in that in the presence of such a disturbing signalthe transmission of the transmitted pulse is shifted by a predeterminedtime which preferably corresponds to the fixed time interval presentbetween two transmitted pulses in the disturbance-free case; and in thatthe transmission of the transmitted pulse after even this time only thentakes place when a disturbing signal has not been found shortly beforeit, etc.
 5. Method in accordance with claim 1, characterised in that atransmitted pulse is first transmitted when no disturbing signals werefound in several time intervals which respectively correspond to thenormal time interval between two transmitted pulses shortly before theexpiry of these times.
 6. Method in accordance with claim 1,characterised in that on detecting a disturbance with periodic characterduring the disturbed light receiving periods between the transmittedlight pulses the transmission of the light pulses is effected such thatit takes place in the center region of the disturbance-free periods. 7.Method in accordance with claim 1, characterised in that the change ofthe disturbing signal is determined with respect to its amount anddirection in that the changing disturbing signal is preferablyinvestigated with respect to two different thresholds (29, 30; 53; 56),or by means of a differentiation element (35), with the transmission ofa transmitted pulse only then taking place when the disturbing signalreduces, with that value of the disturbing signal preferably beingextrapolated where the disturbing signal should reduce to zero, and withthe transmission of the transmitted pulse first taking place after thisvalue.
 8. Method in accordance with claim 1, characterised in that thereceived signal of the light receiver is time-averaged over a long timeafter a transmitted pulse and in that the next transmitted pulse is onlytriggered when after a predetermined time since the last transmittedpulse this signal falls beneath a predetermined value.
 9. Method inaccordance with claim 1, characterised in that the response thresholdfor the detection of a disturbing signal lies substantially lower thanthe response threshold of the received signal processing stage (24). 10.Optical sensor arrangement for detecting articles present in a monitoredregion comprising a pulsed light transmitter which transmits lightpulses having a time spacing one after the other into the monitoredregion, and a light receiver which is so arranged relative to the lighttransmitter and the monitored region that in the absence of articles tobe detected in the monitored region it receives at least substantiallyno light from the light receiver, but on the presence of an article tobe detected in the monitored region receives so much light from thelight transmitter through reflection or transmission that a receivedsignal processing stage connected to the light receiver transmits anarticle detection signal, characterised in that a disturbance detectionstage (16; 46) is also connected or connectable to the light receiver(13) and causes, on detecting reception of a variable disturbing signal,a subsequent transmitted pulse influencing or trigger stage (15) totrigger the transmission of the next transmitted pulse by the pulsegenerator (17) activated by the transmitted pulse influencing or triggerstage (15) only after the actual or probable end of the varyingdisturbing signal, and in that a controlled change-over switch (25) isinserted in the path between the light receiver (13) and the receivedsignal processing stage (24) and is so switched, that it connects thelight receiver (13) with the received signal processing stage (24) onlyon the transmission of a transmitted pulse by the pulse transducer (17)but in contrast, in the pause between two transmitted pulses connectsthe light receiver (13) at least shortly before the triggering of thenext transmitted pulse, preferably however during the entire timeinterval between the sending of two sequential transmitted pulses, tothe disturbance detection stage (16; 46) or to the transmitted pulseinfluencing or trigger stage (15).
 11. Optical sensor arrangement inaccordance with claim 10, characterised in that a clock generator (23)with a frequency of a higher order of magnitude than the normal lightpulse frequency digitises the received signal; in that the individualreceived pulses formed in this way are investigated in the transmittedpulse influencing or trigger stage (15) for the presence or absence of adisturbance; and in that the triggering of a transmitted pulse in thepulse transducer (17) is caused via the transmitted pulse influencing ortrigger stage (15) when no disturbance has been found with apredetermined number of preferably sequential received pulses. 12.Optical sensor arrangement in accordance with claim 11, characterised inthat the transmitted pulse influencing or trigger stage includes a pulsestep down stage (42) connected to the clock generator (23) which firsttriggers a transmitted pulse only after a plurality of in particular 50to 100 clock pulses; and in that on the occurrence of only one disturbedreceived pulse the disturbance detection stage (16, 46) prevents theinitiation of a transmitted pulse through the pulse step down stage(42), or through the transmitted pulse influencing or trigger stage(15), until the predetermined number of undisturbed received pulses hasbeen found.
 13. Optical sensor arrangement in accordance with claim 11,characterised in that the clock generator (23) clocks a digitalintegrator (16) connected to the transmitted pulse influencing ortrigger stage (15) representing the disturbance detection stage, withthe clocked received signal which is evaluated in accordance withdisturbance or non-disturbance being connected to the digital integratorand with the latter causing the transmitted pulse influencing or triggerstage (15) to initiate a transmitted pulse in the pulse transducer (17)only on the presence of a specific number of disturbance-free receivedpulses, with the digital integrator (16) in particular being reset tozero after the occurrence of only a single disturbed received pulse andwith a transmitted pulse only then being triggered when the digitalintegrator (16) has counted a predetermined number (N) of undisturbedreceived pulses.
 14. Optical sensor arrangement in accordance with claim13, characterised in that the output signal of a likewise clockedcomparator (48) with a fixed threshold (69) to which the received pulsesare supplied is connected to the resetting input (I) of the digitalintegrator (16).
 15. Optical sensor arrangement in accordance with claim10, characterised in that the output signal of a preferably clockedcomparator (48), to which a two stage threshold signal (58) is suppliedfrom the disturbance detection stage (46), is applied to the disturbancedetection stage (46) and switches to and fro between two thresholdvalues (57, 62) when the disturbed signal only falls short of the upperthreshold (53) and switches to the lower threshold value (62) when thesignal also does not reach the lower threshold (56); and in that thetransmitted pulse (45) is only triggered thereafter, and indeedpreferably that much later the longer the disturbing signal adopts avalue between the two thresholds (53, 56).
 16. Optical sensorarrangement in accordance with claim 10, characterised in that thetransmitted pulse trigger stage (15) has, following an amplifier (34)fed by the light receiver (13), two comparators (27, 28) with differentthresholds (29, 30) and connected in parallel, wherein, when thereceived signal forms short of the upper threshold (30) an internalsignal increase is triggered in a subsequent threshold time circuit (31)with an attached comparator (33) and wherein, on also falling short ofthe lower threshold (29), an external signal output to the comparator(33) is effected which continuously reduces from the achieved signalincrease value, and in particular decreases linearly, and in that atransmitted pulse is triggered only when the external signal of thethreshold timing circuit (31) falls short of the threshold (32) of thecomparator (33).
 17. Optical sensor arrangement in accordance with claim10, characterised in that it has, following an amplifier (34) which isfed by the light receiver (13), a first comparator (36) with a firstthreshold (39) and connected in parallel with a differentiating circuit(35), the outputs of which are supplied to the two inputs of a sampleand hold circuit (37) which follows a voltage current converter (61)with a subsequent charging element, in particular a capacitor (38),which, on achieving a predetermined voltage, causes, via a comparator(59) with a threshold (40), the transmission in the transmitted pulseinfluencing or trigger stage (15) of a transmitted pulse trigger signalto the pulse generator (17).
 18. Optical sensor arrangement inaccordance with claim 10, characterised in that the transmitted pulseinfluencing and trigger stage (15) is acted on by a mean value formingstage (41), for example in the form of a low pass filter, providedfollowing an amplifier (34) fed by the light receiver (13), with themean value forming stage triggering a transmitted pulse in the pulsegenerator (17) via the transmitted pulse influencing or trigger stage(15) when, after a specific time since the last transmitted pulse, themean value falls below a predetermined threshold (43).
 19. Opticalsensor arrangement in accordance with claim 10, characterised in that amissing pulse detection stage (54) is provided which triggers an alarmdevice (55) in the absence of a transmitted pulse within a predeterminedtime interval after the transmission of the last transmitted pulse.